A regular vertical computer mainframe as shown in FIG. 7, comprises mainly a front panel 1, a shell 2, casing 3, and a diskdrive mounting frame 4. The casing 3 is made in rectangular shape disposed in vertical, having a side panel 32 for mounting the master board. The diskdrive mounting rack 4 is mounted inside the casing 3 near the front side thereof for holding diskdrives and other parts. The shell 2 is shaped like a channel plate covered over the top and two opposite lateral sides of the casing 3. The front panel 1 is covered over the front side of the casing 3, having an opening 11 for loading diskdrive onto the diskdrive mounting rack 4, a power switch 12, and a plurality of function keys 13. The diskdrive mounting rack 4 is made in as an integral part having one side bent into a stepped wall and therefore, the width of the upper part of the diskdrive rack 4 is relatively bigger than that of the lower part thereof. The diskdrive mounting rack 4 further comprises two outwardly coupling flanges 41 bilaterally disposed at the top. The outward coupling flanges 41 have round holes 411 connected to respective round holes 31 on the top wall of the casing 3 by screws 5. When installed, a big chamber 4a and a small chamber 4b are defined between the diskdrive mounting rack 4 and the casing 3.
Regular commercially available diskdrives and the related floppy disks, hard disks, or CD-ROMs are internationally standardized. In order to make a hard diskdrive slidable in a computer mainframe, a box is generally needed and installed in the diskdrive mounting rack for allowing the hard diskdrive to be drawn in and out of the box. However, attaching a sliding box to a hard diskdrive greatly increases the installation space of the hard diskdrive.
In the vertical computer mainframe, the small chamber 4b of the diskdrive mounting rack 4 is designed for holding a 3.5 inch floppy diskdrive and a CD-ROM. Auxiliary memory devices may be installed in the big chamber 4a and the small chamber 4b subject to the depth thereof. In order to install a sliding hard diskdrive, the hard diskdrive must be matched with a box. However, if a box is provided for allowing a hard diskdrive to be drawn in and out, the box must be installed in the big chamber 4a (because the width of the small chamber 4b does not allow the box to be inserted into the small chamber 4b). When a box is installed in the big chamber 4a to hold a hard diskdrive for allowing it to be moved in and out of the box, the loading space of the big chamber 4a for holding a 5.25 inch floppy diskdrive and a CD-ROM becomes occupied by the box. When the diskdrive mounting rack 4 is installed in a regular mini type vertical computer mainframe, the big chamber 4a can hold a 5.25 inch floppy diskdrive and a CD-ROM or two 5.25 inch floppy diskdrive, and the small chamber 4b can hold a 3.5 inch floppy diskdrive or a 3.5 inch hard diskdrive. Because of the limitation of the width, the small chamber 4b is not applicable for holding a 5.25 inch floppy diskdrive or a CD-ROM. If the big chamber 4a is occupied by a box for loading a sliding hard diskdrive, the diskdrive mounting rack 4 will have no room for mounting any 5.25 inch floppy diskdrive or CD-ROM.